1. Field of the Invention
This invention relates to a method of improving the magnetic properties of cobalt substituted magnetite by inducing uniaxial anisotropy in the material in addition to the already present cubic anisotropy. Magnetic recording and storage devices having a film of cobalt substituted magnetite may be used for storing digital information used by data processing computers, or any other analog or digital information where magnetic storage is desired.
2. Description of the Prior Art
It is known by those skilled in the art that heating cobalt substituted magnetite material to an elevated temperature less than the Curie temperature of the material while the material is being subjected to a magnetic field will result in a uniaxial anisotropy being induced in the material in the direction of the magnetic field. The magnetic field applied during heating of the material does not directly induce the resulting uniaxial anisotropy of the material, but merely aligns the magnetization of each crystal or each domain in substantially the same direction. It is understood that when the material is subjected to an elevated temperature less than the Curie temperature, a uniaxial anisotropy is induced in each crystal of a polycrystalline material or each domain of a single crystal whether or not a magnetic field is applied. If the magnetic field is not applied, the uniaxial anisotropy of each crystal or domain is induced in a random direction. The uniaxial anisotropy superimposes itself on the normal cubic anisotropy. Additional information on this phenomena is available in the following publications: Physical Review, Volume 99, page 1788, 1955, by R. M. Bozorth, E. F. Tilden, and A. J. Williams; Proceedings of the Institute of Electrical Engineering, London, Volume 104, Part B -- Supplement 7, page 412, 1957, by Wijn, Van der Heide, and Fast; Journal of the Physical Society of Japan, Volume 13, page 58, 1958, by Shuichi Lida, Hisashi Sekizawa, and Yoshimichi Siyama; Physical Review, Volume 108, page 271, 1957, by R. F. Penoyer and L. R. Bickford, Jr.; and Journal of Applied Physics, Volume 29, page 441, 1958, by L. R. Bickford, Jr., J. M. Brownlaw and R. F. Penoyer.
Cobalt substituted magnetite materials have previously been used in the fabrication of some types of magnetic devices such as permanent magnets. The magnetic qualities of such devices have been improved by heating them to an elevated temperature below the Curie temperature while they were subjected to a magnetic field. However, using such a technique to improve the magnetic qualities of magnetic recording and storage devices is made very difficult, if not impossible, by practical considerations since magnetic recording and storage devices are ordinarily in the shape of a tape, drum, rod or disk. To improve the magnetic properties of a drum shaped device, for example, the uniaxial anisotropy must be oriented circumferentially around the drum axis along the cylindrical walls, and to improve the magnetic properties of a disk shaped device the uniaxial anisotropy must be oriented circularly around the axis on the disk surface. Providing magnetic fields to achieve the desired orientation of the uniaxial anisotropy of such devices while they are being heat treated presents very difficult practical problems.